1. Field of the Invention
The present invention relates to an index position detector for a spindle motor which rotates rotating recording media such as floppy disks, and also relates to a motor apparatus including the index position detector.
2. Description of the Related Art
With regard to spindle motors which rotate rotating recording media, for example, floppy disks, an index signal which provides one pulse for each rotation is required to determine the starting point for writing data. The index signal is also used for detecting the rotational condition of the floppy disk, or the motor, so as to provide a ready signal for writing or reading. In addition, the index signal is also used to start writing in the process of formatting tracks, and to stop the writing when the rotation stops.
FIGS. 10 to 12 conceptually show a construction of a motor apparatus including an index position detector which detects the index position of the spindle motor. Referring to the figures, the motor apparatus includes a mount 101, a circuit board 102 which is mounted on the mount 101, and a rotor yoke 103. The mount 101 is constructed of a metal plate, and is provided with three attachment tabs 101a at the periphery thereof. Each of the attachment tabs 101a is formed unitarily with the mount 101 and is bent upward in an L-shape. In addition, the attachment tabs 101a are provided with attachment holes 101b for fixing the mount 101 to a housing of a floppy disk drive (FDD) by screws or by other means. The mount 101 is also provided with four restraining hooks 101c at the periphery thereof. The restraining hooks 101c are shaped approximately like the letter L and project upward. As shown in FIGS. 10 and 11, a part of each of the restraining hooks 101c is bent in the horizontal direction so as to press downward and hold the circuit board 102, which is disposed on the mount 101.
The circuit board 102 is constructed with an insulated substrate on which wiring patterns and circuit components such as a driver circuit and a driver control circuit (not shown) are mounted. The circuit board 102 is provided with a bearing hole 102a at the center thereof, through which a bearing 104 having a shaft hole 104a is inserted. The bearing 104 is attached to the mount 101, and is provided with an iron-core member 105. The iron-core member 105 has twelve pole pieces 105a which are arranged radially at even intervals, and stator coils 106 are formed around the pole pieces 105a. The stator coils 106 may be divided into three types for applying three phases, U-phase, V-phase, and W-phase. Three coil terminals 106a for the three types of the stator coils 106 and one common coil terminal 106b are soldered on lands 102b provided on the circuit board 102. The iron-core member 105 is constructed of, for example, a laminated iron core formed by punching out a plurality of magnetic steel plates, such as ferrosilicon plates, and stacking them. In addition, a Hall device 107 for detecting the index position of a rotating recording media is mounted on the circuit board 102, so as to oppose one of the pole pieces 105a. 
As shown in FIGS. 13 and 14, the rotor yoke 103 has a shape like a shallow dish inverted on the circuit board 102, including a flange portion 103a at the periphery thereof. A ring-type rotor magnet 108 is affixed on the inner wall of the flange portion 103a. The rotor magnet 108 is constructed of a resin, such as a rubber or a plastic, containing magnetic material. The rotor magnet 108 is equally divided along the periphery thereof into, for example, sixteen portions, which are magnetized so as to alternate S-pole and N-pole. In addition, a window portion 103b having a predetermined width is formed in the flange portion 103a. A pair of dipolar magnets 108a and 108b is provided to the rotor magnet 108 so as to project out through the window portion 103b beyond the periphery of the flange portion 103a. Alternatively, the dipolar magnets 108a and 108b may be separated from the rotor magnet 108 and be stuck on the periphery of the rotor magnet 108.
The rotor yoke 103 is also provided with a shaft 109 which penetrates through the center thereof, and the lower side of the shaft is inserted through the shaft hole 104a formed in the bearing 104. Accordingly, the rotor yoke 103 is rotatably disposed above the circuit board 102 as shown in FIG. 10 so as to cover the stator coils 106, in a manner such that the Hall device 107 opposes the flange portion 103a at the periphery thereof. Although not shown in the figures, a thrust bearing is disposed under the shaft hole 104a so as to support the shaft 109 at the bottom end. Thus, the shaft 109 can smoothly rotate while being supported by the shaft hole 104a and the thrust bearing. In addition, a chucking device for receiving and holding the floppy disk at the center hub thereof (not shown in the figure) is mounted on the rotor yoke 103.
The operation of the index position detector for the spindle motor will be described below. First, a three-phase AC power supply applies a three-phase alternating current to the stator coils 106 of three types for U-phase, V-phase and W-phase, by switching the current in a predetermined order. Accordingly, magnetic opposing force is continuously generated between the stator coils 106 and the rotor magnet 108, so that the rotor yoke 103 rotates above the circuit board 102, which is a part of the stator. The switching of the current is performed by detecting the rotational position using position detectors, for example, three Hall devices disposed between the stator coils 106, and by using the detection signal as a switching control signal.
When the rotor yoke 103 of the spindle motor rotates as described above, the dipolar magnets 108a and 108b also rotate along with the rotation of the rotor yoke 103. Accordingly, the dipolar magnets 108a and 108b periodically move toward and away from the Hall device 107. When the dipolar magnets 108a and 108b are away, the Hall device 107 receives a small amount of magnetic flux, so that the detection output is approximately 0. When the dipolar magnets 108a and 108b are in proximity, the Hall device 107 receives sufficient magnetic flux, so that the detection output increases or decreases in accordance with the movement of the dipolar magnets 108a and 108b. The detected output Vf obtained from the Hall device 107 is calculated by Vf=k"PHgr", so that the detection output Vf is proportional to an amount of the magnetic flux which affects the Hall device 107, as shown in FIG. 15. The detection output is then compared with a predetermined reference voltage to obtain a square wave signal representing the result of the comparison. The square wave signal is used for generating an index signal which provides a pulse at the same time when, for example, the square wave signal provides a rising edge.
The conventional index position detector for the spindle motor, however, has the following problems. That is, an expensive Hall device 107 is required for detecting the magnetic flux from the dipolar magnets 108a and 108b with high sensitivity. In addition, the window portion 103b must be formed in the flange portion 103a of rotor yoke 103, and the end portions of the dipolar magnets 108a and 108b must project far beyond the window portion 103b. Accordingly, high processing cost is incurred when the dipolar magnets 108a and 108b are combined with the rotor magnet 108. When the dipolar magnets 108a and 108b are independently provided, and are affixed on the ring-type rotor magnet 108, there is also a problem in that the gap loss of the magnetic flux density occurs, which degrades the detection sensitivity of the Hall device 107. Additionally, variations in the ambient temperature result in variations in the amplitude of the magnetic flux detection signal and thus a corresponding change in the detection sensitivity of the detector.
Accordingly, it is an object of the present invention to provide an index position detector for a spindle motor which is free from the above-described problems, and which realizes the detection of the index position by using the rotor yoke with a simple and cost-saving construction which includes the conventional window portion. It is also an object of the present invention to provide an index position detector having a stable magnetic flux detection signal amplitude and detection sensitivity with regard to the ambient temperature. In addition, it is another object of the present invention to realize high-precision determination of a starting point for writing data on a rotating recording media.
For attaining the above-described objects, an index position detector for a spindle motor according to the present invention includes a rotor yoke with a flange portion having an inner surface, a rotor magnet which is provided on the inner surface of the flange portion of the rotor yoke, a window portion formed in the flange portion such that a part of the rotor magnet faces outside, and an inductor which is disposed in a stator section to oppose the periphery of the flange portion and which detects a magnetic flux of the rotor magnet via the window portion.
According to the present invention, the high-sensitivity inductor directly receives the magnetic flux from the part of the rotor magnet which is facing outside via the window portion formed in the flange portion of the rotor yoke. Thus, the index signal is more reliably obtained based on the detection output from the inductor at low cost by using the conventional rotor yoke.
The inductor may be disposed to oppose the periphery of the flange portion such that the central axis of a coil contained in the inductor is approximately parallel to the tangential direction of the periphery of the rotor yoke.
Accordingly, the magnetic flux of the rotor magnet more efficiently affects the inductor via the window portion, so that the sensitivity of the magnetic flux detection by the inductor is increased. Thus, reliability of the index signal generation is also increased.
According to another aspect of the present invention, a motor apparatus comprises a circuit board which is disposed above a mount, a rotor yoke which is rotatably supported by the mount, a rotor magnet which is provided to an inner surface of a flange portion of the rotor yoke, stator coils which are disposed between the rotor yoke and the mount and which are arranged radially around the rotational center of the rotor yoke, lands which are provided on the circuit board at positions between the stator coils to connect coil terminals of the stator coils, and an inductor which is mounted on the circuit board to oppose the periphery of the flange portion and which detects a magnetic flux of the rotor magnet via the window portion. The circuit board is formed so as not to expand over one side of the mount relative to the rotational center of the rotor yoke.
Since the circuit board is formed within one side of the mount, the area of the circuit board is reduced, so that the motor is smaller and lighter than the conventional motor. To form the circuit board within one side of the mount, the coil terminals of the stator coils are connected to the lands which are provided on the circuit board at positions between the stator coils.
In addition, the magnetic flux of the rotor magnet more efficiently affects the inductor via the window portion, so that the sensitivity of the magnetic flux detection by the inductor is increased. Thus, reliability of the index signal generation is also increased.
The lands on which the coil terminals of the stator coils are soldered are provided on the circuit board on which the inductor is mounted, and the area of the circuit board is less than half the area of the mount.
Accordingly, the area of the circuit board is reduced. Thus, the circuit board may be more easily attached to the mount, and a smaller motor may be manufactured at a low cost.
According to the present invention, such a construction is applied so that a part of the rotor magnet disposed inside the rotor yoke faces outside through the window portion via the flange portion. The magnetic flux of the rotor magnet affects, through the window portion, the inductor which is disposed at the periphery of the rotor. Thus, high-sensitivity and low-cost detection of the index position is possible, and an index signal having large amplitude is obtained without using hall sensors or providing the rotor magnet with dipolar magnets. Accordingly, a timing process of, for example, determining the starting point for data recording on the rotating recording media, is realized with high precision.
In addition, the inductor is disposed to oppose the flange portion such that the central axis of the coil contained in the inductor is approximately parallel to the tangential direction of the rotor yoke. Accordingly, the coil in the inductor may be affected by a weak magnetic flux emanating from parts deeper inside the rotor magnet compared to the part close to the window portion of the rotor yoke, which increases the precision of the index position detection.
In addition, the lands on which the coil terminals of the stator coils with which the spindle motor is constructed are connected to the lands which are provided on the circuit board on which the inductor is mounted. Thus, the area of the circuit board may be reduced to less than half the area of the metal mount. Accordingly, the circuit board may be more easily attached to the mount, and the cost for the circuit board may be reduced. In addition, the entire body of the index position detector and the spindle motor may be lighter and smaller.